Conventionally, an lens barrel to be attached to a camera includes: a fixed cylinder that is fixed to the camera in a state where it is attached to the camera; a cam cylinder that rotates about the fixed cylinder; and a plurality of lens groups that move in an optical axis direction by the rotation of the cam cylinder (e.g. see Japanese Laid-open Patent Publication No. 2000-89086).
On a design, such a lens barrel has various restrictions in order to secure optical performance. It is desirable to simplify the structure in the lens barrel, in order to secure the optical performance under the restrictions.